Engine Trouble Bogging past 1/2 Throttle

Discussion in '2-Stroke Engines' started by Djskizy, Nov 12, 2014.

  1. Djskizy

    Djskizy New Member

    Ok so heres the scoop. My name is Seth im new here by the way. Lurked for a long time. (finally built a kit), Anywho...
    66cc (flying horse) 2014
    NT carb
    Stock plug
    Notched piston on intake side
    High flow air filter
    20:1 with full synthetic amsoil
    All on a huffy 29er
    Otherwise stock
    Have about 200 miles on the bike at this point

    So I was putt'in along today to put this thing threw its paces and all was fine for the first 8 miles of my 10 mile trip. When all the sudden the bike started bogging like it was out of fuel. I pull over and inspect the bike and find the air filter membrane to be soaked in gas/oil. I removed the filter and got back on to find that the bike would at least run but now wont run past 1/2 throttle under load. I limped it home and inspected the spark plug. It is a flat black color and remains dry. (lean) so i clean it off check the gap and re install. No such luck the problem is sitll there.
    The bike idles fine
    Under no load (Clutch in) revs to the moon and back.
    I cant figure out for the life of me why its acting this way and the proble came up mid ride and nothing seems changed. Ive checked for vacuum leeks and have confirmed there are none.
    Fuel filter is clean
    Air filter is clean
    Its not 4 strokeing (Definite bog)
    Im at a loss. I have some experience building 2 stroke engines but maybe im missing something

  2. crassius

    crassius Well-Known Member

    look for oil seeping out at head gasket or bottom of barrel or along the seam of the case halves

    re-tighten as needed

    in some cases, you might need to check seals too, but it is usually head studs or case bolts
  3. Purple Haze

    Purple Haze Active Member

    I know this sounds silly, but have you checked to see if your choke is on? Sometimes, the nut that holds the lever on will come loose, causing the choke to move around uncontrollably. If that isn't the problem, then Crassius is right. The stock head nuts are very soft, and will lose torque, causing the head gasket to leak. Or, one of the crank seals has popped out, usually the thin one behind the magnet. Before you pull the magnet, just remove the cover, if it's leaking you'll see, if it's dry, replace cover and move on.
  4. Timbone

    Timbone Active Member

    I was suffering from a similar problem. I found that I could get advance by adding choke (which increases air intake) - a condition that normally would cause the engine to bog down. I removed the air filter -which was soaked with fuel!- and thoroughly dried and cleaned it. Now the engine is running better than ever.

    Also: get a NGK spark plug! It's only a few bucks and relatively easy to find. It will make a world of difference and it will take the spark plug out of the problem solving equation.

    Good luck!
  5. Djskizy

    Djskizy New Member

    Ok so I checked the head nuts and they were a little loose i torqued them down to the recommended 15ft/lbs and threw in a ngk b6hs plug and now i have more than half throttle but now the bike seems slow. It previously would do 45mph now it feels like i lost about 10mph. Thanks for all who replayed. I think i can tinker with it a bit more to get it back to full health.
    I know this little nt carb has to go Ive heard mixed suggestions on bigger carbs. I plan on adding a reed valve and doing the jug modifications to support. What is the best carb i can buy for this thing. Im going for quality in this build so... I live in a rural part of Arizona so im full throttle a lot of the time and do need speed.
  6. Purple Haze

    Purple Haze Active Member

    With a reed valve, the Walbro is the best. They have infinite adjustability without disassembly. For a stock type engine, the small Mikunis are quite good. Stay away from the CNS, unless you love working on carbs all the time. Living in Az. you'll want to add a better head, such as the fred head from CR Machine. They provide better performance through higher compression, but their main advantage is cooling. A good exhaust system is a must and provides the most "bang for the buck" IMHO. These are very buzzy little engines, so anything you can do to balance them will be a great help to performance and reliability, I recommend the Jaguar CDI which has a true 2 stroke advance curve.
  7. Djskizy

    Djskizy New Member

    Ahh Thanks,
    I plan on adding a CRMachine head as i like there quality of products. I also plan on taking the rotating assembly and truing it on a lath. I hate how unbalanced these things are. If it vibrates my bones that hard threw the bike i cant imagine what its doing to bearings (another thing i plan to upgrade).